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Refactor pid, random seed and start time initialization.

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Background workers, including parallel workers, were generating
the same sequence of numbers in random().  This showed up as DSM
handle collisions when Parallel Hash created multiple segments,
but any code that calls random() in background workers could be
affected if it cares about different backends generating different
numbers.

Repair by making sure that all new processes initialize the seed
at the same time as they set MyProcPid and MyStartTime in a new
function InitProcessGlobals(), called by the postmaster, its
children and also standalone processes.  Also add a new high
resolution MyStartTimestamp as a potentially useful by-product,
and remove SessionStartTime from struct Port as it is now
redundant.

No back-patch for now, as the known consequences so far are just
a bunch of harmless shm_open(O_EXCL) collisions.

Author: Thomas Munro
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/CAEepm%3D2eJj_6%3DB%2B2tEpGu2nf1BjthCf9nXXUouYvJJ4C5WSwhg%40mail.gmail.com
This commit is contained in:
Thomas Munro
2018-10-19 13:59:14 +13:00
parent e74dd00f53
commit 197e4af9d5
8 changed files with 37 additions and 62 deletions
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2
src/include/miscadmin.h
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@ -25,6 +25,7 @@
#include <signal.h>
#include "datatype/timestamp.h" /* for TimestampTZ */
#include "pgtime.h" /* for pg_time_t */
@ -163,6 +164,7 @@ extern PGDLLIMPORT int max_parallel_workers;
extern PGDLLIMPORT int MyProcPid;
extern PGDLLIMPORT pg_time_t MyStartTime;
extern PGDLLIMPORT TimestampTz MyStartTimestamp;
extern PGDLLIMPORT struct Port *MyProcPort;
extern PGDLLIMPORT struct Latch *MyLatch;
extern int32 MyCancelKey;